Final (Java): Difference between revisions

Revision as of 21:16, 15 January 2006

Revision as of 14:25, 1 February 2006

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In the [[Java programming language]], the <code>'''final'''</code> [[Keyword (computer)|keyword]] is used in several different contexts to define an entity which cannot later be changed.

{{Wikify}}

A '''final class''' cannot be [[Subclass (computer science)|subclassed]]. This is done for reasons of security or efficiancy. Accordingly, many of the Java standard library classes are final, for example [http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html java.lang.System] and <code>[[java.lang.String]]</code>. All [[Method (computer science)|methods]] in a final class are implicitly final.

Final keyword is used in several different contexts as a modifier meaning that what it modifies cannot be changed in any sense.

A '''final method''' cannot be [[Method overriding (programming)|overridden]] by subclasses. This is done for reasons of efficiancy, since the method can then be placed [[Inline function|inline]] whereever it is called.

Final classes:

For example,

A '''final [[variable]]''' is a [[constant]]. It must be assigned a value at [[declaration]], and the variable can later be used but not assigned a new value. Local variables (for example, variables in loops) cannot be declared final.

class Sample

[[Category:Java programming language]]

{

----

----

}

This means that this class will not be subclassed.It provides benfit for security and thread safety.

String class is defined final to prevent creating a subclass.

If you try to access the class(which is declared as final class) , then you will get a compiler error.

Final Method:

You can use the final keyword in a method declaration to indicate that the method cannot be overridden by subclasses.

For example, the object class has some methods as final and some are not.

Final Fields:

When a field is declared final, it is treated as a constant. and cannot be changed.

If you try to change the value,then, compile time error or an exception is generated.

For example:

class Myclass

{

final int n=10;

}

class My

{

public static void main(String args[])

{

Myclass m = new Myclass();

System.out.println("Constant value is "+m.n);

}

}